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Trans Black Sea Region Symposium on Applied Electromagnetism

CPT effect and its applications for weak electromagnetic field detection

C. Andreeva, Yordanka V. Dancheva, G. Alzetta, A. Rossi, S. Cartaleva

Published Nov 11, 2002• 0 citations
Publisher

Abstract

Summary form only given. We have performed experimental investigations of the coherent population trapping (CPT) phenomenon at a single hyperfine transition at the D/sub 1/ and D/sub 2/ lines of Rb in a cell, inserted inside a magnetic shield. For observation of CPT dark resonances at a single hyperfine transition the Zeeman degeneracy has to be removed. This was achieved by applying a homogeneous magnetic field H/sub 1/, parallel to the laser beam and scanned in both directions around zero value. Additional coil produced constant magnetic or RF electromagnetic field H/sub 2/ perpendicular to the beam propagation. The fluorescence signal was registered in order to investigate the influence of the additional electromagnetic field on the dark line parameters. It was observed that the width and the contrast of the dark line are very sensitive to the applied field H/sub 2./ Increasing the value/amplitude of H/sub 2/ causes increase of the width and decrease of the contrast of the CPT resonances.

DOI
10.1109/aem.2000.943249

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Summary form only given. We have performed experimental investigations of the coherent population trapping (CPT) phenomenon at a single hyperfine transition at the D/sub 1/ and D/sub 2/ lines of Rb in a cell, inserted inside a magnetic shield. For observation of CPT dark resonances at a single hyperfine transition the Zeeman degeneracy has to be removed. This was achieved by applying a homogeneous magnetic field H/sub 1/, parallel to the laser beam and scanned in both directions around zero value. Additional coil produced constant magnetic or RF electromagnetic field H/sub 2/ perpendicular to the beam propagation. The fluorescence signal was registered in order to investigate the influence of the additional electromagnetic field on the dark line parameters. It was observed that the width and the contrast of the dark line are very sensitive to the applied field H/sub 2./ Increasing the value/amplitude of H/sub 2/ causes increase of the width and decrease of the contrast of the CPT resonances.
Interaction of a resonant laser beam with an atomic absorption medium creates population redistribution and interference between atomic levels. This anisotropy of the medium is experimentally observed as coherent population trapping (CPT) or electromagnetically induced transparency (EIT). Due to the small sub-natural width of the CPT and EIT resonances, they find wide applications in metrology, quantum optics, atom cooling. A non-compensated stray magnetic field (SMF) can change the shape and sign of the resonance or destroy it completely. In this work, we present an experimental and theoretical investigation of the influence of a stray magnetic field on the CPT resonances obtained on Zeeman sublevels of the D 1 line of 87 Rb in a paraffin-coated vacuum cell. The role is clarified of the polarization moments with different rank in creating the integral registered fluorescent signal in the presence of a stray magnetic field. It is shown that a transverse magnetic field plays an important role in changing the shape of the signal.
Coherent population trapping (CPT) resonances on the degenerate two-level system of the (Fg=2→Fe=1) transition of the 87Rb D1 line were investigated in an uncoated vacuum cell by means of level-crossing type experiments-sweeping a magnetic field around zero value and using a single laser beam. The two-photon resonance manifests itself as fluorescence canceling when the system of levels is degenerate (at zero point of magnetic field). The influence of weak transverse magnetic fields on the amplitude and width of the resonance was investigated. The CPT resonances were observed with linear, circular and elliptical polarized laser light. Transverse magnetic field widens the resonances obtained by linear and circular polarization but splits the resonance created by slightly elliptically polarized laser light. The dependence of this splitting on the elliptical ratio and experimental geometry were investigated. Due to its narrow width and sensitivity to low magnetic fields (< 1 G) this resonance is very promising for small magnetic field measurement.
In this communication we present experimental investigation of coherent effects at Zeeman sublevels of hyperfine levels of Rb in dependence on the polarization of the pumping laser field in order to obtain more complete information about the dark and bright CPT resonances. The coherent effects are examined in Hanle effect configuration, exciting Rb vapor cell with a single-frequency diode laser. By means of phase-sensitive detection (PSD) the amplitude and sign of the CPT resonances are registered in the vicinity of the Rb D1 and D2 lines. It is shown that the sign of the CPT resonances changes when the polarization of the exciting beam changes. Theoretical calculations are performed for the population losses of the given transition in order to clarify the observed experimental results.
We consider the coherent-population-trapping (CPT) phenomenon in a sodium atomic vapor. The experiment leading to the first observation of CPT is revisited with an improved experimental setup and a larger range of magnetic-field strengths. From the analysis of the ground-state hyperfine splitting as a function of the applied magnetic field, we conclude that we have observed the whole spectrum of dark resonances within the D1 line corresponding to the nonabsorbing coherent superposition of two Zeeman sublevels of two different components of the 32S1/2 level. This was not obvious a priori because the transition probabilities at high magnetic-field strengths, as applied in the experiment, have to be taken into account. The differences in the contrast of the various black lines are explained in terms of pumpings outside the interaction scheme preparing the nonabsorbing state. Possible applications of CPT in high magnetic fields are discussed.
Coherent population trapping (CPT) resonances in the degenerate two-level system of the Fg = 2 → Fe = 1) transition of the 87Rb D1 line were investigated in an uncoated vacuum cell by means of Hanle effect configuration. CPT signals with complex shape (narrow resonance approximately 2 mG superimposed on the wide one approximately 150 mG) were observed. The influence of weak transverse magnetic fields (0-1.2 G) on the amplitude and width of the two components was measured. The observed narrow resonances are interesting for application in high resolution spectroscopy and magnetometry.
Coherent Population Trapping (CPT) resonance obtained with linearly polarized laser beam through magnetic field sweep (Hanle configuration) was investigated in 87Rb D1 line. Influence of the coherence due to high-rank polarization moment (hexadecapole moment), created in the medium, on the CPT resonance shape was calculated and experimentally detected in fluorescence. It was observed as an inverted structure at a high power of excitation. To distinguish resonances due to coherence between Zeeman sub-levels with ΔmF=2 from that with ΔmF=4, the Larmour frequency ωLmodulated by applying an a.c. magnetic field (a.c. MF). Resonance signal at frequency corresponding to 4ωL observed in a fluorescence, and after lock-in on the frequency corresponding to frequency difference between sub-levels ΔmF=4.